1. Field of the Invention
The present invention relates generally to an ink-jet printing apparatus ejecting an ink toward a printing medium and an ejection recovery method of a printing head. More particularly, the invention relates to an ink-jet printing apparatus ejecting an ink and a liquid for making a coloring agent in the ink insoluble or coagulated, and an ejection recovery method of a printing head in the printing apparatus.
It should be noted that the present invention is applicable for all of devices or apparatus using a printing media, such as papers, clothes, non-woven fabrics, OHP sheets and the like (hereinafter occasionally referred to as "media"). More particularly, applicable devices may be business machines, such as a printer, a copy machine, facsimile machine and so on, a mass-production equipment, such as a textile printing machine or the like, and so on, for example.
2. Description of the Related Art
Conventionally, an ink-jet printing apparatus performing printing for a printing medium, such as paper, cloth, plastic sheet, OHP sheet and so on (hereinafter occasionally referred to as "media") can perform high density and high speed printing operation. Therefore, such ink-jet printing apparatus can be used as a printer to be used as an output device in a copy machine, a facsimile machine, an electronic typewriter, a word processor, a work station and the like, or as a handy or portable printer to be provided for a personal computer, a host computer, an optical disk device, a video device and so on. Also, such ink-jet printing apparatus has been commercialized.
In this case, the ink-jet printing apparatus takes a construction corresponding to a particular function of the apparatus, mode of use and so on. In general, the ink-jet printing apparatus includes a carriage mounting a printing head and an ink tank, a transporting means for transporting a printing paper as a printing medium, and control means for controlling the components set forth above. By scanning the printing head ejecting ink droplets from a plurality of ejection openings in a direction (primary scanning direction) perpendicular to a transporting direction of the printing paper (auxiliary scanning direction) and transporting the printing paper in an amount equal to a printing width of the printing head at an interval between scan, for printing over the entire printing paper. This method performs printing by ejecting an ink toward the printing paper from the printing head depending upon a print signal, and has been used as a printing system of low running cost and gentle for low noise. Also, in such system, by using the printing head, in which a plurality of nozzles for ejecting the ink are aligned in the auxiliary scanning direction, it becomes possible to make a printing width of scan at one time greater and whereby to achieve speeding up of printing.
Furthermore, recently, an apparatus mounting a plurality of printing heads corresponding to three to four colors of inks and performing a full-color printing, has been put into practice. Typically, in such apparatus, four kinds of printing heads corresponding to inks of three primary colors of yellow (Y), magenta (M) and cyan (C), and, in addition, black (K), and ink tanks are mounted.
However, upon formation of a color image on a plain paper by the conventional ink-jet printing method and an apparatus, prevention of bleeding of the inks between respective colors of black, yellow, magenta and cyan, and increasing of density of black image and prevention of feathering are mutually contradictory tasks. Therefore, a difficulty is encountered in obtaining high density image without causing bleeding or feathering.
Normally, upon printing of the color image on the plain paper by the ink-jet printing method, a quick drying ink having high penetration speed into the plain paper is used. Therefore, in a boundary region of respective colors forming the image, bleeding of the inks can be prevented. However, when quick drying ink is used, density of the black image becomes low. On the other hand, color image portions other than black become low in color development ability. Furthermore, upon printing of line image typically characters or the like, so-called feathering to cause bleeding of the ink along fiber of the paper can be caused. Particularly, feathering of characters printed by black ink can be easily perceived in comparison with other color to be the unclear characters for insufficient sharpness. As a result, as a whole, quality of the printed image can be significantly degraded.
In general, in order to obtain high quality image with high density of a black image portion and without causing feathering, it is required to deposit an ink having relatively low penetration speed into the plain paper at large amount in certain extent. However, in this case, bleeding of the black ink and the color ink can be caused at an interface portion between black image portion and the color image portion to degrade quality of the printed image.
In order to improve the foregoing drawback, a system obtain a color image of high color development with no bleeding, by promoting drying of the ink by providing a heater within the printing apparatus, and has been commercialized.
However, in this system, it is inherent that the apparatus becomes bulky and high cost.
As set forth above, prevention of bleeding between black and other colors, and achieving high density of the black image and prevention of feathering have been contradictory tasks inherently require trade off therebetween.
Therefore, in Japanese Patent Application Laid-open No. 3-146353 (1991), for example, there has been proposed a system not to effect printing for a region along an interface between a printing regions of the black ink and the color ink. However, in this system, a drawback is encountered in causing variation of the printed data. On the other hand, in Japanese Patent Application Laid-open No. 4-158049 (1992), there has been proposed a method for performing printing by switching a plurality of heads for color printing and a head for character printing. In this method, when the black image printed by the color printing heads and the black image printed by the character printing head are present in admixing manner, unpleasant sensation should be caused due to difference of printing quality of the black images. Furthermore, a method for preventing bleeding in a black region along the boundary between the printed regions printed by black ink and the color ink, by overlapping printing of the color ink, has been considered. In principle, while black can be obtained by overlaying three primary colors Y, M and C (color mixing). However, in most case, the black image formed by color mixing of the color inks has lower color development than the normal black image formed by the black ink.
On the other hand, in Japanese Patent Applications Laid-open Nos. 56-84992 (1981) and 64-63185 (1989), technologies using a liquid making dye in the ink insoluble have been disclosed.
Amongst, in Japanese Patent Application Laid-open No. 56-84992, a method to preliminarily apply a material for fixing the dye on a printing paper has been disclosed. However, in the method, particular printing paper has to be used. Also, in order to preliminarily apply the material for fixing the dye, it is inherent that the apparatus becomes bulky and high cost. Furthermore, it is difficult to stably apply the material on the printing paper in a predetermined thickness.
On the other hand, in Japanese Patent Application Laid-open No. 64-63185 (1988), a technology for depositing an achromatic ink for making the dye insoluble on the printing paper by an ink-jet printing head, has been disclosed. According to the disclosure, since the dot of the achromatic ink is formed to have greater diameter than the dot formed by an image forming ink, a desired printing characteristics can be satisfied even when offset is cased between depositing positions of the achromatic ink and the image forming ink.
Furthermore, in Japanese Patent Application Laid-open No. 7-195823 (1995), color printing by one path of the printing head is permitted by applying an achromatic precursor on the surface of the printing medium in advance of ink-jet printing.
As set forth above, the methods disclosed in the foregoing publications hold problems to be solved. However, since the dye in the ink is made insoluble, bleeding between respective color inks may be prevented.
The applicant of the present application has already proposed an ink-jet printing method which can solve the problems set forth above and achieving low running cost by restricting consumption of an ink which make a dye insoluble. With the proposed printing method, superior water resistance than prior art can be achieved even on the plain paper, higher density image can be obtained. Furthermore, as applied for color printing, an image of high color development without bleeding between colors can be obtained.
However, in the conventional ink-jet printing apparatus using a liquid making the image forming ink insoluble (hereinafter referred to as "processing liquid"), it is possible that a mixture (hereinafter referred to as "mixture mist") of the image forming ink (hereinafter simply referred to as "ink") and the processing liquid deposits in the vicinity of a nozzle array of the printing head for ejecting the ink or the processing liquid. In such case, the processing liquid and the ink may react to generate a solidified substance to be a cause of ejection failure of the ink or the processing liquid.
Conventionally, there has not been known any ejection recovery method which can effectively prevent generation of the mixture mist on the nozzle or therearound, and effectively remove the generated mixture mist in order to keep high quality printing for a long period.